The present invention relates generally to surgical procedures for spinal stabilization and more specifically to instrumentation adapted for inserting a spinal implant within the intervertebral disc space between adjacent vertebrae. More particularly, while there may be other applications, the present invention is especially suited for engaging two vertebral bodies that are offset in an anterior-posterior fashion, as in spondylolisthesis, with respect to each other and providing a protected passageway for the movement of instruments and implants therethrough.
Currently available systems utilize a hollow sleeve having a uniform bone engaging end with teeth extending therefrom to be driven into the vertebrae adjacent the disc space. However, a common condition in spinal abnormalities is that adjacent vertebral bodies have been displaced creating an anterior-posterior offset condition. While offset vertebral bodies may be encountered in any part of the spine as a result of trauma, disease, or degeneration, the condition of spondylolisthesis typically develops in the lumbar spine. With offset vertebral bodies, the uniform bone engaging end of the hollow sleeve in prior systems, adapted to engage anterior-posterior aligned vertebral bodies, fails to completely engage both offset vertebra bodies simultaneously. This incomplete engagement with the offset vertebral bodies creates an unprotected space between one of the vertebral bodies and the end of the hollow sleeve. This unprotected space may allow contact between instruments disposed within the sleeve, such as cutting instruments, and surrounding tissue. Such contact may damage the sensitive tissue adjacent to the vertebral body leading to potential injury or death for the patient.
While the more recent techniques and instrumentation represent an advance over earlier surgical procedures for protecting surrounding tissue during preparation of the disc space and insertion of a fusion device, the need for improvement still remains. The present invention is directed to this need and provides a more effective protective guide sleeve for engaging offset vertebral bodies.